1. Field of the Invention
The present invention relates to a roller bearing which can infinitely perform a rectilinear motion.
2. Description of the Prior Art
There are roller bearings for an infinite rectilinear motion in which a number of rollers roll in the infinite circulating passage which is constituted such that both ends of the rectilinear load track and return passage are coupled by the direction turning passages. In such bearings, it is known that the number of rollers existing on the load track surface varies between n and n+1 in association with the rolling of the rollers. Therefore, the load supporting force per unit supporting area to the load track surface and, accordingly, the elastic deformation amounts of the track surface and rollers change due to a load change. Thus, during the running, mechanical parts supported and fixed to the bearing are slightly lifted up when the load condition changes from the state in that the number of rollers is small, namely, the elastic deformation amounts are large to the state in that the number of rollers is large, that is, the elastic deformation amounts are smaller. On the contrary, the mechanical parts slightly fall when the load condition varies from the state whereby the number of rollers is large to the state whereby it is small.
The above-mentioned vertical motion (hereinafter, referred to as a running deformation) of the running mechanical parts is very rare. However, for example, in the case where the foregoing bearing is used in a machine tool and the parts of the machine are run and moved, a working accuracy of the machine tool is changed even due to an extremely slight running deformation, so that it is a remarkable obstacle.
To solve the above problem, as shown in the Official Gazette of Japanese Patent Examined Publication No. 2206/1981 (U.S. Pat. No. 3,797,897), there has been known a roller bearing in which wedge-shaped notch portions are formed at the center of both ends in the moving direction of the rolling members on the load track surface. Such a bearing has an effect of reduction of the running deformation amount and also has a function to correct the rollers inclined from the location that is perpendicular to the progressing direction at both ends of the load track surface and thereby to eliminate the gradient. However, this roller bearing has a drawback such that the rollers which roll and come from the no-load range to the load range serving as the load track surface suddenly collide with the remaining portion of the load track surface other than the foregoing notch portion in the edge portion in the moving direction of the rolling members on the load track surface, so that the running deformation amount is enlarged due to this collision.
On one hand, as a technology such that the balls gradually come into contact with the load track surface and the elastic deformation amount is gradually increased and thereby allowing the balls to be smoothly moved, there has been known a technology such that a gentle slope range and a steep slope range are continuously formed in the load track surface (Japanese Utility Model Examined Publication No. 50176/1981). According to this technology, a remarkable effect can be derived by use of the balls which can roll in any directions. On one hand, in case of the roller bearing in which the gentle slope range and steep slope range are formed as mentioned above, an effect of a certain degree can be obtained as compared with the roller bearing in which such slope ranges are not formed. However, the rollers which freely roll in the infinite circulating passage without a holding apparatus enter the load range from the no-load range while complicatedly moving in the actual condition. Consequently, such a technology is practically insufficient to reduce the running deformation.
Although both of those well-known technologies have the slight effects for the running deformation as mentioned above, in the case where the parts of a particularly precise machine tool are moved and run, the running deformation amount reaches a few .mu.m to tens of .mu.m. Therefore, this value is unsatisfactory as a running deformation amount of the roller bearing for an infinite rectilinear motion for use in a high precise machine tool.